Radio communication terminal and radio communication method

ABSTRACT

Provided is a radio communication terminal which is capable of measuring quality in communication with a handover destination with high accuracy. The radio communication terminal is capable of communicating with a base station or a relay node, and includes: a receiver which receives control information including information relating to measurement of measuring quality of a neighbor cell; an extractor which extracts information on a subframe where the measurement should be performed, which is a subframe where only transmission of a signal from the relay node connected to the base station is performed, from the information relating to the measurement; a measurement section which performs the measurement, on a subframe basis, based on the extracted information on the subframe where the measurement should be performed; and a transmitter which transmits a result of the measurement to the base station or the relay node.

TECHNICAL FIELD

The present invention relates to a radio communication terminal and aradio communication method which transmit and receive data to and from abase station.

BACKGROUND ART

The 3GPP (3rd Generation Partnership Project) which is an internationalmobile communication standardization group has started thestandardization of LTE-Advanced (Long Term Evolution-Advanced, LTE-A) asa fourth generation mobile communication system. As disclosed in NonPatent Literature 1, in LTE-A, a relay technology of relaying radiosignals by using a relay node (RN) has been studied with the goals ofcoverage expansion and capacity improvement.

The relay technology will be described with reference to FIG. 12 . FIG.12 is a diagram illustrating a system which relays radio signals usingthe relay technology. In FIG. 12 , eNB represents a base station, RNrepresents a relay node, and UE represents a radio communicationterminal. Further, UE1 represents a radio communication terminalconnected to eNB, and UE2 represents a radio communication terminalconnected to RN.

Here, in LTE-A, RN having an individual cell ID as in eNB is beingstudied, and thus, when viewed from UE, RN can also be regarded as onecell like eNB.

eNB is connected to a network by wired communication, whereas RN isconnected to eNB by wireless communication. A communication channelconnecting between RN and eNB is called a backhaul channel. On the otherhand, a communication channel connecting between eNB or RN and UE iscalled an access channel.

A radio relay system in a downlink channel (Down Link, DL) will bedescribed with reference to FIG. 12 . FIG. 12 is a diagram illustratinga radio relay system in the related art. RN receives signals from eNB inthe backhaul channel. Further, RN transmits signals to UE2 in the accesschannel of RN.

Here, when the backhaul channel and the access channel are allocated inthe same frequency bandwidth, if RN performs transmission and receptionat the same time, loop-back interference occurs. For this reason, RNcannot perform transmission and reception at the same time. Thus, inLTE-A, a relay method is being studied in which the backhaul channel andthe access channel of RN are allocated while being divided by the timedomain (on a subframe basis).

A relay method in the related art in which a backhaul channel and anaccess channel of RN are allocated while being divided by the timedomain (on a subframe basis) for allocation will be described withreference to FIG. 13 . FIG. 13 is a diagram illustrating a subframeconfiguration of a downlink channel in the relay method in the relatedart. Reference signs [n, n+1, . . . ] in FIG. 13 represent subframenumbers. Boxes in FIG. 13 represent subframes of the downlink channel,and represent transmission subframes of eNB, reception subframes of UE1,transmission subframes of RN and reception subframes of UE2.

As shown in FIG. 13 , eNB transmits signals in all the subframes.Further, UE1 receives signals in all the subframes. Further, as shown inFIG. 13 , RN transmits signals in the subframes except for the subframenumbers [n+2, n+6]. UE2 can receive signals in the subframes except forthe subframe numbers [n+2, n+6]. Furthermore, RN receives signals fromeNB in the subframes of the subframe numbers [n+2, n+6].

As described above, in RN, the subframes of the subframe numbers [n+2,n+6] serve as the backhaul channel of RN, and the other subframes of thesubframe numbers [n, n+1, n+3, n+4 and n+5] serve as the access channelof RN.

However, if RN transmits no signal in the subframes where RN serves asthe backhaul channel, a problem occurs that a measurement operation ofmeasuring the quality of RN does not function at UE of LTE which has notascertained the presence of RN.

As a method of solving this problem, in LTE-A, using an MBSFN(Multicast/Broadcast over Single Frequency Network) subframe defined inLTE is being considered.

The MBSFN subframe is a subframe which is prepared to realize an MBMS(Multimedia Broadcast and Multicast Service) service in the future. TheMBSFN subframe is designed to transmit cell-specific control informationat the first two symbols and transmit signals for the MBMS in thedomains of the third and subsequent symbols of the MB SFN subframe.

Here, the LTE terminal is capable of performing measurement by using thefirst two symbols in the MBSFN subframe. Thus, the MBSFN subframe isused in a pseudo-manner in the RN cell, and RN is capable of using theMB SFN subframe as the reception subframe of the backhaul channel.Specifically, RN transmits the control information specific to the RNcell at the first two symbols of the MB SFN subframe, and does nottransmit data for the MBMS but receives signals from eNB in the domainsof the third and subsequent symbols of the MB SFN subframe.

In this description, the MBSFN subframe as mentioned above will becalled an “MBSFN subframe that RN uses as the backhaul”.

In this regard, in a mobile communication system, a situation occurs inwhich, when UE communicates with a certain eNB, received power from eNBis lowered due to movement of UE, change in the surrounding environmentor the like and thus UE cannot maintain communication with eNB.

To cope with such a situation, UE can be re-connected to eNB or RN whichis higher in received power than eNB in communication therewith, tothereby maintain communication. This is called handover.

Hereinafter, eNB or RN will be also called a “cell”, and a cell whichcommunicates with UE will be also called an “own cell”.

In order to perform the handover, it is necessary that UE measuressignal power from a cell which is present in the vicinity of the cell incommunication therewith (the cell which is present in the vicinity ofthe own cell may be called a neighbor cell). In the 3GPP LTE, a processof measuring signal power or signal quality from this neighbor cell iscalled measurement.

In the measurement, a cell instructs UE to measure received power orquality from a neighbor cell, and UE measures the received power fromthe neighbor cell and notifies the own cell of the measurement result.UE performs the measurement using a reference signal (RS) or asynchronization signal generated on the basis of a cell-specific series.

In the measurement of LTE, as disclosed in Non Patent Literature 2, UEmeasures RSRP (Reference Signal Received Power) or RSRQ (ReferenceSignal Received Quality) using a cell-specific reference signal.

CITATION LIST Non Patent Literature

-   Non Patent Literature 1: 3GPP TR36.814 v0.4.1 (2009-02) Further    Advancements for E-UTRA Physical Layer Aspects (Release 9)-   Non Patent Literature 2: 3GPP TS36.214 v8.6.0 (2009-03) Physical    layer—Measurements (Release 8)

SUMMARY OF INVENTION Technical Problem

In LTE, as measurement in a case where an MBSFN subframe is present, thefollowing operations are performed, for example. Firstly, a cellnotifies UE, which is under the control of the cell, of the position ofthe MBSFN subframe in SIB2 (System Information Block 2) which notifiessystem information.

As described above, since the MBSFN subframe is originally prepared torealize the MBMS service, UE, in particular, UE in LTE recognizes thatthe MBSFN subframe is also present in the neighbor cell, in the MBSFNsubframe of the own cell. Thus, UE is capable of performing ameasurement operation suitable for the MB SFN subframe, in the MB SFNsubframe of the own cell. For example, UE may perform measurement usingonly the first two symbols, may not perform measurement in the MBSFNsubframe, or may perform similar operations.

In LTE-A, when RN uses the MBSFN subframe as the backhaul, there is acase where the position of the “MBSFN subframe that RN uses as thebackhaul” is different in each RN. In this case, a subframe which is notthe MBSFN subframe of the own cell serves as the MBSFN subframe in aneighbor RN.

Here, the neighbor RN does not transmit signals so as to receive signalsfrom eNB in the domains of the third and subsequent symbols of the“MBSFN subframe that RN uses as the backhaul”. In a case where RN whichdoes not transmit signals in the “MBSFN subframe that RN uses as thebackhaul” is not a target cell of measurement in UE, if no signal istransmitted from the corresponding RN, it is seen on the side of UE thatinterference in signals from the target cell is reduced.

If UE performs measurement of the target cell in a state where theinterference in the signals from the target cell is reduced, a problemarises that an error occurs between quality based on the measurementresult and actual quality in which interference is present. For example,if UE recognizes that the quality based on the measurement result issuperior to the actual quality and performs handover, there is a problemin that a cell which is a handover destination cannot achieve athroughput expected on the basis of the measurement result by UE.

An object of the present invention is to provide a radio communicationterminal and a radio communication method which are capable of measuringquality in communication with a handover destination with high accuracy.

Solution to Problem

The present invention provides a radio communication terminal which iscapable of communicating with a base station or a relay node, the radiocommunication terminal including: a receiver which receives controlinformation including information relating to measurement of measuringquality of a neighbor cell; an extractor which extracts information on asubframe where the measurement should be performed, which is a subframewhere only transmission of a signal from the relay node connected to thebase station is performed, from the information relating to themeasurement; a measurement section which performs the measurement on asubframe basis, based on the extracted information on the subframe wherethe measurement should be performed; and a transmitter which transmits aresult of the measurement to the base station or the relay node.

In the radio communication terminal the extractor extracts informationon a subframe which is the subframe where the measurement should beperformed and is not an MBSFN subframe used as a backhaul in the relaynode connected to the base station, from the information relating to themeasurement, and the measurement section performs the measurement in thesubframe which is not the MBSFN subframe.

In the radio communication terminal, the receiver receives the controlinformation including the information relating to the measurement ofmeasuring the quality of the neighbor cell including the information onthe subframe where the measurement should be performed, from the basestation or the relay node which is a connection destination of the radiocommunication terminal.

In the radio communication terminal, the extractor extracts informationon a subframe which is the subframe where the measurement should beperformed and is not an MBSFN subframe used as a backhaul in a relaynode which is the relay node connected to the base station and belongsto a relay node group including a plurality of neighbor relay nodes,from the information relating to the measurement, and the measurementsection performs the measurement on a subframe basis on the basis of theextracted information on the subframe.

The present invention also corresponds to a radio communication terminalwhich is capable of communicating with a base station or a relay node,the radio communication terminal including: a receiver which receives areference signal of a neighbor cell and control information relating tothe radio communication terminal; an extractor which extractsinstruction information for performing measurement of measuring qualityof the neighbor cell, from the control information; a detector whichdetects a subframe where the measurement should be performed using thereference signal of the neighbor cell based on the extracted instructioninformation; a measurement section which performs the measurement in thedetected subframe where the measurement should be performed; and atransmitter which transmits a result of the measurement to the basestation or the relay node.

The present invention also corresponds to a radio communication terminalwhich is capable of communicating with a base station or a relay node,the radio communication terminal including: a receiver which receives areference signal of a neighbor cell, information relating to measurementof measuring quality of the neighbor cell and control information on theradio communication terminal; a first extractor which extracts, on asubframe basis, position information on a first subframe which is acandidate where the measurement should be performed in a relay nodewhich is the relay node connected to the base station and belongs to arelay node group including a plurality of neighbor relay nodes, from theinformation relating to the measurement; a detector which measuresreceived power on a subframe basis in the relay node group based on theextracted position information on the first subframe and the referencesignal of the neighbor cell, and detects the relay node group which hasthe smallest change in a result of the measurement for the receivedpower; a second extractor which extracts information on a secondsubframe which is not an MBSFN subframe used as a backhaul in the relaynode which belongs to the detected relay node group; and a measurementsection which performs the measurement, on a subframe basis, based onthe extracted information on the second subframe.

The present invention also provides a radio communication method used ina radio communication terminal which is capable of communicating with abase station or a relay node, the radio communication method including:receiving control information including information relating tomeasurement of measuring quality of a neighbor cell; extractinginformation on a subframe where the measurement should be performed,which is a subframe where only transmission of a signal from the relaynode connected to the base station is performed, from the informationrelating to the measurement; performing the measurement on a subframebasis, based on the extracted information on the subframe where themeasurement should be performed; and transmitting a result of themeasurement to the base station or the relay node.

The present invention also provides a radio communication method used ina radio communication terminal which is capable of communicating with abase station or a relay node, the radio communication method including:receiving a reference signal of a neighbor cell and control informationrelating to the radio communication terminal; extracting instructioninformation for performing measurement of measuring quality of theneighbor cell, from the control information; detecting a subframe wherethe measurement should be performed using the reference signal of theneighbor cell based on the extracted instruction information; performingthe measurement in the detected subframe where the measurement should beperformed; and transmitting a result of the measurement to the basestation or the relay node.

The present invention also provides a radio communication method used ina radio communication terminal which is capable of communicating with abase station or a relay node, the radio communication method including:receiving a reference signal of a neighbor cell, information relating tomeasurement of measuring quality of the neighbor cell and controlinformation on the radio communication terminal; extracting, on asubframe basis, position information on a first subframe which is acandidate where the measurement should be performed in a relay nodewhich is the relay node connected to the base station and belongs to arelay node group including a plurality of neighbor relay nodes, from theinformation relating to the measurement; measuring received power in therelay node group, on a subframe basis, based on the extracted positioninformation on the first subframe and the reference signal of theneighbor cell, and detecting the relay node group which has the smallestchange in a result of the measurement for the received power; extractinginformation on a second subframe which is not an MB SFN subframe used asa backhaul in the relay node which belongs to the detected relay nodegroup; and performing the measurement on a subframe basis, based on theextracted information on the second subframe.

Advantageous Effects of Invention

According to the radio communication terminal and the radiocommunication method of the present invention, as UE performsmeasurement for handover in subframes, which are not used as thebackhaul in a plurality of RNs connected to one eNB, where signals fromthe plurality of RNs are transmitted, it is possible to measure qualityin communication with a handover destination with high accuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a radio relay system according to afirst embodiment of the present invention.

FIG. 2 is a diagram illustrating downlink subframes in FIG. 1 .

FIG. 3 is a diagram illustrating a bit map of subframes wheremeasurement is performed in FIG. 2 .

FIG. 4 is a diagram illustrating subframes where measurement isperformed in FIG. 2 .

FIG. 5 is a block diagram illustrating a configuration of a radiocommunication terminal 100 according to the first embodiment.

FIG. 6 is a block diagram illustrating a configuration of a base stationapparatus 200 according to the first embodiment.

FIG. 7 is a block diagram illustrating a configuration of a radiocommunication terminal 500 which is a modification of the radiocommunication terminal 100.

FIG. 8 is a diagram illustrating a radio relay system according to asecond embodiment of the present invention.

FIG. 9 is a diagram illustrating downlink subframes in FIG. 8 .

FIG. 10 is a block diagram illustrating a configuration of a basestation apparatus 400 according to the second embodiment.

FIG. 11 is a block diagram illustrating a configuration of amodification of a radio communication terminal according to the secondembodiment.

FIG. 12 is a diagram illustrating a radio relay system in the relatedart.

FIG. 13 is a diagram illustrating a configuration of downlink subframesin a relay method in the related art.

MODES FOR CARRYING OUT INVENTION First Embodiment

Hereinafter, a first embodiment of the present invention will bedescribed with reference to FIGS. 1 to 7 .

Firstly, a radio relay system in the first embodiment of the presentinvention will be described. FIG. 1 is a diagram illustrating the radiorelay system according to the first embodiment of the present invention.In FIG. 1 , eNB represents a base station (base station apparatus) 200,RN1 and RN2 represent relay stations 310 and 320, and UE represents aradio communication terminal 100, respectively.

Hereinafter, in the first embodiment, the radio communication terminal100 is referred to as UE, the base station 200 is referred to as eNB,and the relay stations 310 and 320 are referred to as RN1 and RN2,respectively.

Hereinafter, in the first embodiment, as studied in LTE-A, RN1 and RN2have an individual cell ID, in a similar way to eNB. Thus, when viewedfrom UE, RN1 and RN2 may be considered as one cell, respectively, in asimilar way to eNB.

Hereinafter, in the first embodiment, as studied in LTE-A, a relaymethod of dividing a backhaul channel and an access channel of RN bytime domains (on a subframe basis) for allocation is used.

Here, in the radio relay system shown in FIG. 1 , errors occurredbetween quality based on a measurement result and actual quality in ahandover destination are considered. The errors include a first errordue to inferiority of the measurement result to the actual quality and asecond error due to superiority of the measurement result to the actualquality.

As an example of occurrence of the first error, there is a case wherecharacteristics expected on the basis of the measurement result cannotbe obtained, even though the handover destination is determined on thebasis of the measurement result. Further, in a case where the actualquality of the handover destination is much inferior to the measurementresult, the characteristics are inferior compared with the time beforehandover is performed. Alternatively, there is a case that UE cannotmaintain communication.

On the other hand, as an example of occurrence of the second error,there is a case where characteristics superior to the characteristicsexpected on the basis of the measurement result can be obtained in thehandover destination. As the errors between the measurement result andthe actual quality of the handover destination, the first error has asignificant influence on the radio relay system shown in FIG. 1 ,compared with the second error. Thus, it is preferable to avoid theoccurrence of the first error.

Accordingly, in a case where the quality of the handover destination ischanged, if UE performs measurement in the case of the worst quality toinform eNB of the result, it is possible to avoid the above-describedfirst error.

Here, the worst quality refers to quality based on the measurementresult in a case where interference is the strongest due to signalstransmitted from the own cell and a different cell.

That is, at the timing when the neighbor RN1 and RN2 transmit signals,UE may perform measurement. In other words, in subframes which are notan “MB SFN subframe that RN uses as a backhaul” in the neighbor RN1 andRN2, UE performs measurement.

Here, the neighbor RN refers to, in a case where the own cell is RN, anRN to which UE is connected and other RNs connected to eNB to which theRN is connected, and refers to, in a case where the own cell is eNB, RNsconnected to the eNB.

As described above, one characteristic of the present embodiment is thatUE performs measurement of handover in the subframes which are not the“MBSFN subframe that RN uses as the backhaul” in all the neighbor RNs.

Here, the measurement of handover according to the present embodimentwill be described with reference to FIGS. 1 and 2 . FIG. 2 is a diagramillustrating downlink (DL) subframes in FIG. 1 .

In FIG. 2 , eNB transmits signals in all the subframes. Further, RN1sets subframes [n+2, n+6] as the “MBSFN subframes that RN uses as thebackhaul”. Thus, RN1 does not transmit a signal in the subframes [n+2,n+6]. Similarly, RN2 sets a subframe [n+4] as the “MB SFN subframe thatRN uses as the backhaul”. Thus, RN2 does not transmit a signal in thesubframe [n+4].

UE receives all the signals from eNB, RN1 and RN2 in the subframes [n,n+1, n+3, n+5, n+7]. Thus, from the standpoint of UE, the subframes [n,n+1, n+3, n+5, n+7] become subframes in which interference componentsbecome the highest in a case where measurement of the neighbor cells isperformed.

Accordingly, UE performs measurement of the neighbor cells using thesubframes [n, n+1, n+3, n+5, n+7] as the subframes in which themeasurement is performed.

That is, UE performs measurement of the neighbor cells in the subframeswhich are not the “MBSFN subframes that RN uses as the backhaul”, in allthe neighbor RNs.

Hereinafter, an example of a specific method of realizing themeasurement of handover in the present embodiment will be described withreference to FIGS. 2 to 4 .

eNB, RN1 and RN2 notify UE of the subframes where UE should performmeasurement. Then, UE performs measurement in the subframes in whichmeasurement should be performed.

It is necessary that eNB, RN1 and RN2 share the timing of the “MBSFNsubframes that RN uses as the backhaul” among eNB, RN1 and RN2. Thus,eNB, RN1 and RN2 share the position of the “MBSFN subframes that RN usesas the backhaul”.

The position of the “MBSFN subframe that RN uses as the backhaul” isshared among eNB, RN1 and RN2, using control information on RN1 and RN2(including control information on an upper layer).

Further, by notifying position information on the “MBSFN subframe thatRN uses as the backhaul”, relating to other RNs connected to eNB, in thecontrol information on RN1 and RN2, it is possible to share the positioninformation on the “MBSFN subframe that RN uses as the backhaul” in eachRN, even among RN1, RN2 and the other RNs.

That is, eNB, RN1 and RN2 can recognize the position information on thesubframes which are not the “MBSFN subframes that RN uses as thebackhaul” in the neighbor RNs. Accordingly, eNB, RN1 and RN2 can notifyUE of the subframes which are not the “MBSFN subframes that RN uses asthe backhaul” as the subframes where measurement should be performed, inthe neighbor RNs.

As a method of notifying UE of the subframes where measurement should beperformed, for example, a method of notifying the subframes wheremeasurement should be performed by a bit map or a method of tabulatingthe subframes where measurement should be performed to notify an indexof the table, is used.

Notification Method of Subframes—Bit Map

The method of notifying UE of the subframes where measurement should beperformed by a bit map will be described with reference to FIG. 3 . FIG.3 is a diagram illustrating a bit map expression of the subframes wheremeasurement is performed in FIG. 2 .

Here, in FIG. 3 , the subframe numbers [n, n+1, n+7, . . . ] arereplaced with [0, 1, . . . , 7, . . . ]. In a case where the subframesare notified by the bit map, it is difficult to notify all thesubframes. Thus, it is necessary to assign periodicity to the subframesnotified by the bit map to be patterned. A start subframe number of thepattern is set to 0.

For example, as the pattern of the bit map, a pattern including a frameformed by ten subframes or a pattern obtained by connecting theplurality of frames (for example, pattern obtained by connecting fourframes) is used.

In the bit map shown in FIG. 3 , “1” represents subframes wheremeasurement is performed, and “0” represents subframes where measurementis not performed.

Since the subframes where measurement is performed are subframes whichare not the “MBSFN subframe that RN uses as the backhaul” in all theneighbor RNs, the subframes [0, 1, 3, 5, 7, . . . ] become “1” in thebit map pattern, in FIG. 3 . eNB, RN1 or RN2 notifies UE of the bit mappattern “110101011 . . . ” as the subframes where measurement should beperformed, and thus, UE can perform measurement in the subframe numbercorresponding to “1” in the bit map pattern.

Notification Method of Subframes—Tabulation

Next, the notification method by tabulation and using an index will bedescribed with reference to FIG. 4 . FIG. 4 is a diagram illustratingsubframes where measurement is performed using, as an example, the caseof the downlink subframes in FIG. 2 , in a similar way to a case wherenotification is performed by the bit map shown in FIG. 3 .

As shown in FIG. 4 , a table of subframes where measurement is performedis prepared in advance, which is shared among eNB, RN1, RN2 and UE. Forexample, in the “table of subframes where measurement is performed”shown in FIG. 4 , a table number “0” represents that all the subframesare subframes where measurement is performed. Further, a table number“m” represents that the subframes [0, 1, 3, 5, 7, . . . ] are subframeswhere measurement is performed.

In the case of the downlink subframes shown in FIG. 4 , the subframes[2, 6] are the “MB SFN subframes that RN use as the backhaul” in RN1.Further, the subframe [4] is the “MB SFN subframe that RN uses as thebackhaul” in RN2. Accordingly, the subframes [0, 1, 3, 5, 7, . . . ]become subframes where UE performs measurement. As the table number “m”is notified from eNB, RN1 and RN2 to UE under the control thereof, UEcan ascertain the subframes where measurement should be performed, tothereby perform measurement in the subframe.

As described above, in the present embodiment, UE can measure thequality in communication with the handover destination with highaccuracy. Thus, in the present embodiment, it is possible to suppressthe errors occurred between the measurement result and the actualquality of the handover destination, and the UE can achieve thethroughput expected on the basis of the measurement result in thehandover destination.

Configuration of Radio Communication Terminal

Next, a configuration of the radio communication terminal 100 accordingto the first embodiment will be described with reference to FIG. 5 .FIG. 5 is a block diagram of the radio communication terminal 100according to the first embodiment. The radio communication terminal 100shown in FIG. 5 includes an antenna 101, a switch (SW) 103, a receptionRF section 105, a reception processor 107, a neighbor cell signalreception processor 109, a measurement controller 111, a measurementsubframe extractor 113, a measurement section 115, a measurement resultmemory section 117, a measurement report information generator 119, atransmission processor 121, and a transmission RF section 123.

The reception RF section 105 performs filtering processing for signalsreceived by the antenna 101 in order to remove signals except for acommunication bandwidth, performs frequency conversion to an IFfrequency bandwidth or to a baseband, and outputs the resultant signalsto the reception processor 107 and the neighbor cell signal receptionprocessor 109.

The reception processor 107 performs reception processing for thesignals output from the reception RF section 105, separates data andcontrol information which are multiplexed in the received signals, andoutputs them. Specifically, the reception processor 107 converts theanalog signals to digital signals by an AD converter or the like, andperforms demodulation processing, decoding processing and the like.

The neighbor cell signal reception processor 109 performs receptionprocessing for the signals from the neighbor cells, with respect to thesignals output from the reception RF section 105, and outputs the resultto the measurement subframe extractor 113. This process is the sameprocess as in the reception processor 107, but is different therefrom inthat the processing specific to the neighbor cells is performed.Specifically, reception processing for a reference signal or the like isan example of the difference. In LTE, since the reference signal istransmitted in a cell-specific series, the neighbor cell signalreception processor 109 performs reception processing for signalsspecific to the neighbor cells which are the reference signals accordingto the neighbor cell series.

Further, using the output signals of the neighbor cell signal receptionprocessor 109, a necessary signal is output for measuring the quality ofthe neighbor cells in the measurement section 115 at the subsequentstage. For example, in a case where a desired signal component ismeasured, the neighbor cell signal reception processor 109 outputs thereference signal. Further, in a case where an interference component ismeasured, the neighbor cell signal reception processor 109 outputs adata signal.

When instruction information for performing measurement is included inthe control information on the radio communication terminal output fromthe reception processor 107, the measurement controller 111 extractsinformation relating to the subframe where measurement should beperformed from the control information to output the extractedinformation to the measurement subframe extractor 113. Here, as a methodof notifying the subframes where measurement should be performed to theradio communication terminal from eNB, a method of notifying thesubframes where measurement should be performed using the bit mappattern as described with reference to FIG. 3 or a method of tabulatingthe subframes where measurement should be performed to notify an indexof the table as described with reference to FIG. 4 , is used.

On the basis of the information relating to the subframes wheremeasurement should be performed, which is output from the measurementsection 115, the measurement subframe extractor 113 extracts the signalsspecific to the neighbor cells output from the neighbor cell signalreception processor 109 on a subframe basis, to output the result to themeasurement section 115.

The measurement section 115 performs the measurement using the signalsof the neighbor cells extracted by the measurement subframe extractor113, and outputs the result to the measurement result memory section117.

The measurement result memory section 117 stores the measurement resultmeasured by the measurement section 115, and outputs the result to themeasurement report information generator 119.

At the timing when the measurement result is reported to eNB, themeasurement report information generator 119 generates the measurementreport information to be reported to eNB using the measurement resultstored in the measurement result memory section 117, and outputs theresult to the transmission processor 121.

The transmission processor 121 performs transmission processing so thatthe measurement report information generated by the measurement reportinformation generator 119 can be transmitted to eNB, and then outputsthe result to the transmission RF section 123. The transmissionprocessing includes signal multiplexing of transmission data, feedbackinformation or the like, encoding processing, modulation processing, andthe like.

The transmission RF section 123 performs frequency conversion into RFfrequency, power amplification and transmission filtering processing forthe transmission signal which is transmission-processed by thetransmission processor 121, and outputs the result to the antenna 101through the switch (SW) 103.

Next, a configuration of the base station apparatus 200 (eNB) accordingto the present embodiment will be described with reference to FIG. 6 .FIG. 6 is a block diagram illustrating the configuration of the basestation 200 according to the first embodiment. The base stationapparatus 200 shown in FIG. 6 includes a measurement instruction section201, a measurement information generator 203, a signal multiplexer 205,a transmission processor 207, a transmission RF section 209, a switch(SW) 211, an antenna 212, a reception RF section 213, a receptionprocessor 215, a measurement report information extractor 217, and ahandover controller 219.

Transmission data in the figure is transmission data to each UE, whichis input to the signal multiplexer 205. RN information in the figureincludes neighbor RN information which is information relating to theneighbor RNs and includes position information on the “MBSFN subframethat RN uses as the backhaul” in the neighbor RNs, or the like. The RNinformation is input to the measurement information generator 203.

The measurement instruction section 201 instructs the measurementinformation generator 203 to generate measurement information so thatmeasurement of the neighbor cells should be performed by UE in which thehandover is necessary.

The measurement information generator 203 generates the informationrelating to measurement based on the measurement instruction of themeasurement instruction section 201, and outputs the result to thesignal multiplexer 205.

Here, the information relating to measurement includes informationrelating to a subframe where measurement should be performed, which is asubframe which is not the “MBSFN subframe that RN uses as the backhaul”in the neighbor RNs, using the neighbor RN information included in theRN information.

The signal multiplexer 205 multiplexes the input transmission data toeach UE, the control information (not shown), the information relatingto measurement, and the like, and outputs the result to the transmissionprocessor 207. The signal multiplexer 205 arranges the transmission datato each UE to perform user multiplexing, and performs multiplexing withother signals.

The transmission processor 207 performs transmission processing for thesignals multiplexed by the signal multiplexer 205, and outputs theresult to the transmission RF section 209. The transmission processingincludes encoding processing, modulation processing and the like, forexample.

The transmission RF section 209 performs frequency conversion into RFfrequency, power amplification and transmission filtering processing forthe transmission signals which are transmission-processed by thetransmission processor 207, and outputs the result to the antenna 212through the switch (SW) 211.

The reception RF section 213 performs filtering processing for thesignals received by the antenna 212 in order to remove signals exceptfor a communication bandwidth, performs frequency conversion to an IFfrequency bandwidth or to a baseband, and outputs the result to thereception processor 215.

The reception processor 215 performs reception processing for thesignals output from the reception RF section 213, and separates thesignals into the reception data, the control information and the like.Specifically, the reception processor 215 converts the analog signals todigital signals by an AD converter or the like, and performsdemodulation processing, decoding processing and the like.

The measurement report information extractor 217 extracts measurementreport information from the control information separated by thereception processor 215, and outputs the result to the handovercontroller 219.

The handover controller 219 controls handover on the basis of themeasurement report information extracted by the measurement reportinformation extractor 217.

In the present embodiment, eNB, RN1 or RN2 notifies UE of the subframeswhere measurement should be performed, but this is not limitative. Forexample, eNB, RN1 or RN2 may not notify UE of the subframes wheremeasurement should be performed, but UE may detect the subframes wheremeasurement should be performed, to thereby perform measurement.

Here, as a method of detecting the subframes where measurement should beperformed by UE, for example, a method of detecting the subframes wheremeasurement should be performed using the received power or a method ofdetecting the subframes where measurement should be performed byreceiving control information (PDCCH or the like of LTE) about thedownlink transmitted by eNB, RN1 or RN2, is used.

Detection of Subframes where Measurement Should be Performed—ReceivedPower First Example

As a first example of the method of detecting the subframes wheremeasurement should be performed using the received power, the followingmethod is used. Firstly, UE measures the received power over theplurality of subframes, and detects a subframe where the received poweris the largest. UE sets a threshold which becomes a predetermined powerdifference with reference to the largest received power, and detects asubframe where the received power is lower than the threshold as the“MBSFN subframe that RN uses as the backhaul” in the neighbor RNs. UEsets subframes except for the detected “MBSFN subframe that RN uses asthe backhaul” in the neighbor RNs, as the subframes where measurementshould be performed.

For example, where the largest received power of the detected subframeis Pmax, the predetermined power difference is Pd, the threshold is Pth,and the received power of the n-th subframe is Pn, UE detects a subframen which satisfies the following Formula 1 as the “MBSFN subframe that RNuses as the backhaul” in the neighbor RNs.[Formula 1]P _(n) P _(th), (P _(th) =P _(max) −P _(d))  Formula 1

Second Example

Further, as a second example of the method of detecting the subframeswhere measurement should be performed using the received power, thefollowing method may be also used. Firstly, UE measures and averages thereceived power over the plurality of subframes, and detects an averagereceived power. UE sets a threshold which becomes a predetermined powerdifference with reference to the average received power, and comparesthe threshold and the received power of each subframe. Further, UEdetects a subframe where the received power is lower than the thresholdas the “MBSFN subframe that RN uses as the backhaul” in the neighborRNs. UE sets subframes except for the detected “MBSFN subframe that RNuses as the backhaul” in the neighbor RNs, as subframes wheremeasurement should be performed.

For example, where the average received power is Pave, UE detects asubframe n which satisfies the following Formula 2 as the “MBSFNsubframe that RN uses as the backhaul” in the neighbor RNs, in a similarway to Formula 1.[Formula 2]P _(n) <P _(th), (P _(th) =P _(ave) −P _(d))  Formula 2

Third Example

Further, as a third example of the method of detecting the subframeswhere measurement should be performed using the received power, thefollowing method may be also used. Firstly, UE detects the receivedpower in subframes which are not the “MBSFN subframe that RN uses as thebackhaul” in RN1 or RN2. UE sets a threshold which becomes apredetermined power difference with reference to the received power, andcompares the threshold and the received power Pn of each subframe.Further, UE detects a subframe where the received power is lower thanthe threshold as the “MB SFN subframe that RN uses as the backhaul” inthe neighbor RNs. For example, as the subframes except for the “MBSFNsubframe that RN uses as the backhaul”, the subframes having subframenumbers 0, 4, 5 and 9, which are not originally set as the MBSFNsubframe, are set.

For example, when the received power of the subframe which is not the“MBSFN subframe that RN uses as the backhaul” in RN1 or RN2 isPnon-MBSFN, UE detects a subframe n which satisfies the followingFormula 3 as the “MBSFN subframe that RN uses as the backhaul” in theneighbor RNs, in a similar way to Formula 1.[Formula 3]P _(n) <P _(th), (P _(th) =P _(non-MBSFN) −P _(d))  Formula 3

In the cases of the above-described first to third examples, there is acase where signal power from RN which is distant from UE is weak and UEcannot detect the “MBSFN subframe that RN uses as the backhaul” in theRN. However, as RN is distant from UE, interference of RN on UE isreduced. Thus, even though the signal power from RN which is distantfrom UE cannot be received, UE can detect the subframes wheremeasurement should be performed.

Detection of Subframes where Measurement Should be Performed—Receptionof Control Information on DL

The reception processing is performed for control information(specifically, PDCCH or the like of LTE) transmitted from each of eNB,RN1 and RN2 and the control information on RN which becomes the MBSFNsubframe is detected. In this case, the signal power from RN which isdistant from UE is weak, and thus, the control information on the RN maynot be detected, but since the interference from such an RN which isdistant is small, the influence on measurement is insignificant andthere is no problem.

As described above, in the present embodiment, as UE detects thesubframes where measurement should be performed, UE can performmeasurement in consideration of dominant interference. Further, sincethe subframes where measurement should be performed is not necessarilybe notified to UE from eNB, RN1 or RN2, it is possible to reducesignaling overhead.

Modification of UE

Here, a configuration of a radio communication terminal (UE) 500 in acase where the subframes where measurement should be performed aredetected from the received power in the present embodiment will bedescribed with reference to FIG. 7 . FIG. 7 is a block diagramillustrating the configuration of the radio communication terminal 500.The radio communication terminal 500 shown in FIG. 7 is different fromthe radio communication terminal 100 shown in FIG. 5 in that ameasurement subframe detecting section 512 is added. The configurationexcept for this is the same as in the embodiment shown in FIG. 5 , andthe same reference numerals are given to the same elements, and detaileddescription thereof will be appropriately omitted.

The radio communication terminal 500 shown in FIG. 7 includes theantenna 101, the switch (SW) 103, the reception RF section 105, thereception processor 107, the neighbor cell signal reception processor109, the measurement controller 111, the measurement subframe detector512, the measurement subframe extractor 113, the measurement section115, the measurement result memory section 117, the measurement reportinformation generator 119, the transmission processor 121, and thetransmission RF section 123.

When there is an instruction for performing measurement in the controlinformation on the radio communication terminal output from thereception processor 107, the measurement controller 111 instructs themeasurement subframe detector 512 to detect the subframes wheremeasurement should be performed.

The measurement subframe detector 512 detects the subframes wheremeasurement should be performed using the signals output from thereception RF section 105 based on the instruction of the measurementcontroller 111.

For example, as the method of detecting the subframes where measurementshould be performed by the measurement subframe detector 512, the firstto third examples in which the subframes where measurement should beperformed are detected using the received power and the example in whichthe subframes where measurement should be performed are detected byreceiving the control information (PDCCH or the like of LTE) about thedownlink transmitted by eNB, RN1 or RN2, are used.

On the basis of the subframes where measurement should be performeddetected by the measurement subframe detector 512, the measurementsubframe extractor 113 extracts the neighbor cell signals output fromthe neighbor cell signal reception processor 109 on a subframe basis,and outputs the result to the measurement section 115.

The measurement section 115 performs measurement using the neighbor cellsignals extracted by the measurement subframe extractor 113, and outputsthe result to the measurement result memory section 117.

The measurement result memory section 117 stores the measurement resultmeasured by the measurement section 115 and the subframe number of thesubframes where measurement should be performed detected by themeasurement subframe detector 512, and then outputs the result to themeasurement report information generator 119.

The measurement report information generator 119 generates informationto be reported to eNB using the measurement result and the subframenumbers of the subframes where measurement should be performed stored inthe measurement result memory section 117, at the timing when themeasurement result is reported to eNB, and then outputs the result tothe transmission processor 121.

In the present embodiment, the method of directly notifying thesubframes where measurement is performed to UE from eNB, RN1 and RN2 isdescribed, but this is not limitative. eNB, RN1 and RN2 may notify, foreach neighbor RN, the position of the “MBSFN subframe that RN uses asthe backhaul” in the neighbor RNs, and may derive subframes which arenot the “MBSFN subframe which is used as the backhaul” in all the RNs inUE, to thereby specify the subframes where measurement is performed.

In the present embodiment, as the subframes where measurement should beperformed, the subframes which are not the “MB SFN subframe that RN usesas the backhaul” in the neighbor RNs are notified, but this is notlimitative. In a case where the subframes which are not the “MBSFNsubframe that RN uses as the backhaul” in RN are determined, thesubframes may be determined as the subframes where measurement should beperformed. For example, in LTE, subframes [0, 4, 5, 9] are determined inorder not to be set as the MB SFN subframes. Thus, since the subframeswhere measurement should be performed is not necessarily be notified, itis possible to suppress signaling overhead.

In the present embodiment, UE averages the measurement result in thesubframes where measurement is performed over a plurality of times, tothereby enhance the accuracy of measurement.

In the present embodiment, as the subframes where measurement isperformed, the subframes which are not the “MB SFN subframe that RN usesas the backhaul” in the neighbor RNs are determined, but this is notlimitative. For example, in the neighbor eNB, RN1 or RN2, a subframewhere traffic is small and data is not transmitted may be present. Thissubframe is also the same as the MBSFN subframe used as the backhaul inRN in the present embodiment. Thus, it may be considered that thesubframe where traffic is small and data is not transmitted is notincluded in the subframes where measurement is performed.

In the present embodiment, the neighbor RN includes, in a case where theown cell is RN, an RN to which UE is connected and other RNs connectedto eNB to which the RN is connected, and includes, in a case where theown cell is eNB, RNs connected to the eNB, but this is not limitative.For example, the neighbor RN may include RNs connected to a differenteNB. In this case, by exchanging position information on the MBSFNsubframe used as the backhaul of RN connected to each eNB between eNBs,the same operation as in the present embodiment may be performed.

Second Embodiment

Hereinafter, a second embodiment of the present invention will bedescribed with reference to FIGS. 8 to 11 .

Firstly, a radio relay system according to the second embodiment of thepresent invention will be described. FIG. 8 is a diagram illustratingthe radio relay system in the second embodiment of the presentinvention. In FIG. 8 , eNB represents a base station (base stationapparatus) 400, RN1, RN2 and RN3 represent relay stations 610, 620 and630, and UE represents a radio communication terminal 700, respectively.

Hereinafter, in the second embodiment, the radio communication terminal700 is referred to as UE, the base station 400 is referred to as eNB,and the relay stations 610, 620 and 630 are referred to as RN1, RN2 andRN3, respectively.

Hereinafter, in the second embodiment, as studied in LTE-A, RN1 and RN2have an individual cell ID, in a similar way to eNB. Thus, when viewedfrom UE, RN1 and RN2 may be considered as one cell, respectively, in asimilar way to eNB.

Hereinafter, in the second embodiment, as studied in LTE-A, a relaymethod of dividing a backhaul channel and an access channel of RN intotime domains (on a subframe basis) for allocation is used.

Here, in the first embodiment, when the plurality of RNs are present, asthe number of “MB SFN subframes that RN uses as the backhaul” isincreased in all the RNs, the number of subframes where measurement isperformed is reduced, and thus, samples may not be sufficientlyobtained, thereby lowering the accuracy of measurement. On the otherhand, when sufficient samples are obtained to maintain the accuracy ofmeasurement, it may take time for measurement.

Thus, in the second embodiment, when the plurality of RN1, RN2 and RN3are present, it is considered that the amount of interference of each RNon UE changes according to the distance from each RN to UE. That is,since the interference amount on UE is reduced in RN which is distantfrom UE, the influence on measurement is small.

Here, the relationship between the distance from each RN to UE and theinterference amount of each RN on UE will be described with reference toFIGS. 8 and 9 . FIG. 9 is a diagram illustrating subframes of DL in theradio relay system shown in FIG. 8 . In FIG. 8 , UE is connected to eNB.It is assumed that UE is positioned in the vicinity of RN1 and RN2 andthe position of RN3 is distant from UE compared with the positions ofRN1 and RN2.

Referring to FIG. 9 , the positions of the “MBSFN subframes that RN usesas the backhaul” in RN1 are the subframes [n+2, n+6]. The positions ofthe “MBSFN subframes that RN uses as the backhaul” in RN2 are thesubframes [n+4, n+8]. The positions of the “MBSFN subframes that RN usesas the backhaul” in RN3 are the subframes [n+3, n+7].

Since RN3 is distant from UE compared with RN1 or RN2, the amount ofinterference of RN3 on UE is smaller than that of RN1 or RN2. Thus, inthe entire interference amount on UE, the interference amount of RN1 orRN2 which is close to UE is dominant, and the interference amount of RN3which is distant from UE has an insignificant influence in the entireinterference amount.

Since even the “MBSFN subframe that RN uses as the backhaul” in RN3which is distant from UE has an insignificant influence in the entireinterference amount on UE, the “MBSFN subframe that RN uses as thebackhaul” as the subframes where measurement is performed has aninsignificant influence in measurement.

Accordingly, in FIG. 9 , in RN1 and RN2 other than RN3 which is distantfrom UE compared with RN1 and RN2, by notifying UE of the subframes [n,n+1, n+3, n+5, n+7] as the subframes which are not the “MBSFN subframethat RN uses as the backhaul”, UE can ascertain the subframes wheremeasurement should be performed. Further, the number of subframes wheremeasurement should be performed can be increased.

Further, RN1 and RN2 which have dominant interference in the entireinterference amount of each RN on UE are RN1 and RN2 which arepositioned closer to UE than RN3. It can be said that RNs which areclose in distance to each other with reference to one UE are neighborRNs. For example, in FIG. 8 , RN1 is adjacent to RN2, and RN2 isadjacent to RN3, which are close in distance to RN, but RN1 is notadjacent to RN3. Accordingly, it can be said that RN3 which is notadjacent to a different RN is not the dominant interference for one UE.Thus, as shown in FIG. 9 , as a combination of a plurality of RNs whichdo not become the MBSFN subframe, neighbor RNs have only to be used.

Accordingly, the radio relay system according to the second embodimentdetermines the subframes which are not the “MBSFN subframe that RN usesas the backhaul” on the basis of information on the combination of theneighbor RNs when eNB, RN1 or RN2 notifies UE of the subframes wheremeasurement should be performed. As a result, the handover processingand control becomes easy.

On the basis of the above-described relationship between the distancefrom each RN to UE and the interference amount of each RN on UE, UEaccording to the present embodiment groups the neighbor RNs, andperforms measurement of handover in the subframes which are not the“MBSFN subframe that RN uses as the backhaul” in RNs in the group.Hereinafter, a specific method will be described with reference to FIGS.8 and 9 . In FIG. 8 , a set of RN1 and RN2 and a set of RN2 and RN3 areneighbor RN groups, respectively. The set of RN1 and RN2 is referred toas an RN group 1, and the set of RN2 and RN3 is referred to as an RNgroup 2.

Here, referring to FIG. 9 , the subframes [n, n+1, n+3, n+5, n+7] aresubframes which are not the “MBSFN subframes that RN uses as thebackhaul” in RNs which form the RN group 1. Further, the subframes [n,n+1, n+2, n+5, n+6] are subframes which are not the “MBSFN subframesthat RN uses as the backhaul” in RNs which form the RN group 2. Thesesubframes become subframes of each RN group where measurement should beperformed. eNB or each RN exchanges information relating to thepositions of the MBSFN subframes for the backhaul in each RN between eNBand RNs, derives the subframes of each RN group where measurement shouldbe performed, and notifies UE of the subframes where measurement shouldbe performed.

As a specific method in which eNB or each RN notifies UE of thesubframes where measurement should be performed, for example, in asimilar way to the first embodiment, the method of notifying thesubframes by the bit map pattern is used, or the method of tabulatingthe subframes where measurement should be performed to notify the indexof the table is used.

In the second embodiment, since RN3 is positioned distant from UEcompared with RN1 and RN2, UE performs measurement in the subframes ofthe RN group 1 including RN1 and RN2 where measurement is performed.

eNB or each RN gives an instruction to UE with respect to the RN groupused when UE performs measurement. In this case, when eNB or each RN hasascertained the position of UE, eNB or each RN gives an instruction toUE to select the RN group from which RN3 which is distant from UE isremoved and to perform measurement in the subframes of the RN groupwhere measurement should be performed. On the other hand, when eNB oreach RN has not ascertained the position of UE, eNB or each RN notifiesUE of the subframes of each RN group where measurement should beperformed and gives an instruction to UE to perform measurement for allthe RN groups. Alternatively, eNB or each RN gives an instruction to UEto sequentially perform measurement for each RN group.

As described above, in the present embodiment, since the number ofsubframes used for measurement can be secured even when the plurality ofRNs are present, UE can measure the quality in communication with thehandover destination with high accuracy. Thus, it is possible tosuppress occurrence of errors between the quality based on themeasurement result and the actual quality of the handover destination,and UE can achieve throughput expected on the basis of the measurementresult in the handover destination.

Since the configuration of the radio communication terminal 700according to the present embodiment is the same as that of the radiocommunication terminal 100 according to the first embodiment, detaileddescription thereof will be omitted.

Next, the configuration of the base station (base station apparatus) 400according to the present embodiment will be described with reference toFIG. 10 . FIG. 10 is a block diagram illustrating the configuration ofthe base station 400 according to the present embodiment. Here, the basestation 400 shown in FIG. 10 is different from the base station 200shown in FIG. 6 in that RN information input to the measurementinformation generator 203 becomes RN group information. Theconfiguration except for this is the same as in the embodiment shown inFIG. 6 , and the same reference numerals are given to the same elements,and detailed description thereof will be appropriately omitted.

The base station 400 (eNB) shown in FIG. 10 includes the measurementinstruction section 201, the measurement information generator 203, thesignal multiplexer 205, the transmission processor 207, the transmissionRF section 209, the switch (SW) 211, the antenna 212, the reception RFsection 213, the reception processor 215, the measurement reportinformation extractor 217, and the handover controller 219.

The RN group information refers to information relating to an RN groupincluding a combination of a plurality of RNs, such as subframes of eachRN group where measurement should be performed, and is input to themeasurement information generator 203. The subframes of each RN groupwhere measurement should be performed are the subframes which are notthe “subframe where RN uses as the backhaul” in RNs in each RN group.Further, the RN group may use RNs formed at the installation timing orthe like of RNs as they are, or may continuously use RNs which areperiodically formed. As a method of grouping RNs, for example, a methodof combining neighbor RNs for grouping, a method of grouping RNs whichare close in distance, or the like, may be used.

The measurement instruction section 201 instructs the measurementinformation generator 203 to generate the measurement information sothat measurement of a cell adjacent to UE in which the handover isnecessary is performed. At this time, the measurement instructionsection 201 instructs UE to use subframes of a certain RN group wheremeasurement is performed.

The measurement information generator 203 generates control informationrelating to measurement based on the measurement instruction from themeasurement instruction section 201, and outputs the result to thesignal multiplexer 205. As the information relating to the measurement,there is information relating to the subframes of RN group wheremeasurement should be performed indicated by the measurement instructionsection 201.

In the present embodiment, eNB or RN notifies UE of the RN group usedwhen measurement should be performed in UE, but this is not limitative.For example, a method may be used in which eNB or RN notifies UE ofinformation relating to the subframes of the plurality of RN groupswhere measurement should be performed and UE determines the RN group.

Here, a method of determining the RN group in UE will be described withreference to FIG. 9 . Firstly, with respect to all the RN groups, UEperforms measurement of received power for the subframes [n, n+1, n+2,n+3, n+5, n+6, n+7] having the possibility of being the subframes wheremeasurement is performed. Further, measurement results of the receivedpower in the respective subframes are compared with respect to thesubframes where measurement is performed. The RN group 1 includes thesubframes [n, n+1, n+3, n+5, n+7], and the RN group 2 includes thesubframes [n, n+1, n+2, n+5, n+6].

Here, the RN group 1 has a smaller change in the received power in therespective subframes than the RN group 2. Contrarily, the RN group 2 hasa larger change in the received power in the respective subframes thanthe RN group 1. In the case of the RN group 2 in which the change in thereceived power in the respective subframes is large, UE performsmeasurement in the subframes in which a dominant interference componentis not present. Accordingly, UE may detect the RN group 1 in which thechange in the received power in the respective subframes is small.

For example, where the maximum received power in the RN group 1 isPG1_max and the minimum received power is PG1_min, a received powerdifference PG1_D in the RN group 1 is expressed as the following Formula4.[Formula 4]P _(G1_D) =P _(G1_max) −P _(G1_min)  Formula 4

Similarly, with respect to the RN group 2, where the maximum receivedpower is PG2_max and the minimum received power is PG2_min, a receivedpower difference PG2_D in the RN group 2 is expressed as the followingFormula 5.[Formula 5]P _(G2_D) ≅P _(G2_max) −P _(G2_min)  Formula 5

Here, UE may compare the received power difference PG1_D in the RN group1 with the received power PG2_D in the RN group 2, and may detect the RNgroup in which the received power difference is small. In addition tothe difference between the maximum received power and the minimumreceived power in the respective subframes, dispersion or standarddeviation of the received power in the respective subframes, thresholddetermination from an average value thereof, or the like, may be used.Further, the RN group is detected using the received power in therespective subframes, but the measurement result may be used.

Modification of UE

The configuration of UE when UE detects the RN group as described abovewill be described with reference to FIG. 11 . FIG. 11 is a block diagramillustrating the configuration of the modification (UE) of the radiocommunication terminal 700 in the second embodiment. The radiocommunication terminal 900 shown in FIG. 11 includes the antenna 101,the switch (SW) 103, the reception RF section 105, the receptionprocessor 107, the neighbor cell signal reception processor 109, ameasurement controller 710, a measurement candidate subframe extractor711, an RN group detector 712, the measurement subframe extractor 113,the measurement section 115, the measurement result memory section 117,the measurement report information generator 119, the transmissionprocessor 121, and the transmission RF section 123.

The block diagram of UE shown in FIG. 11 is different from the blockdiagram of UE shown in FIG. 5 in that the measurement candidate subframeextractor 711 and the RN group detector 712 are added. The configurationexcept for this is the same as in the embodiment shown in FIG. 5 , andthe same reference numerals are given to the same elements, and detaileddescription thereof will be appropriately omitted.

The measurement controller 710 detects whether an instruction forperforming measurement is included in control information relating tothe radio communication terminal output from the reception processor107. When the instruction for performing measurement is includedtherein, the measurement controller 710 extracts the RN groups and theRN group information relating to the subframes where measurement shouldbe performed from the control information.

Further, the measurement controller 710 outputs information on thepositions of the subframes having the possibility of being candidatesfor the subframes where measurement should be performed to themeasurement candidate subframe extractor 711, from the extractedinformation, and then outputs the RN group information to the groupdetector 712.

The measurement candidate subframe extractor 711 extracts the positioninformation relating to the subframes of the measurement candidates fromthe signal output from the reception RF section 105 on a subframe basis,based on the position information relating to the subframes of themeasurement candidates output from the measurement controller 710, andoutputs the result to the RN group detector 712.

The RN group detector 712 measures the received power on a subframebasis using the signal output from the measurement candidate subframeextractor 711. Further, the RN group detector 712 compares the receivedpower for the subframes of each RN group where measurement should beperformed, and detects an RN group in which change in the received powerin the respective subframes is the smallest. As the detection method ofthe RN group, as described above, UE compares the received powerdifference PG1_D in the RN group 1 with the received power differencePG2_D in the RN group 2, and detects the RN group in which the receivedpower difference is small. Further, in the RN group in which thereceived power changed in the respective subframes is the smallest, theRN group detector 712 outputs information on the subframes in whichmeasurement should be performed to the measurement subframe extractor113.

The measurement subframe extractor 113 extracts a neighbor cell signaloutput from the neighbor cell signal reception processor 109 on asubframe basis, on the basis of the information relating to thesubframes where measurement is performed output from the RN groupdetector 712, and outputs the result to the measurement section 115.

In the present embodiment, UE averages the measurement results in thesubframes where measurement is performed over a plurality of times,thereby making it possible to enhance the accuracy of measurement.

In the present embodiment, as the subframes where measurement isperformed, the subframes which are not the “MBSFN subframe that RN usesas the backhaul” in the neighbor RNs are used, but this is notlimitative. For example, in the neighbor eNB, RN1 or RN2, a subframewhere traffic is small and data is not transmitted may be present. Thissubframe is also the same as the MBSFN subframe used as the backhaul inRN in the present embodiment. Thus, it may be considered that thesubframe where traffic is small and data is not transmitted is not thesubframe where measurement should be performed.

In the present embodiment, the neighbor RN includes, in a case where theown cell is RN, an RN to which UE is connected and other RNs connectedto eNB to which the RN is connected, and includes, in a case where theown cell is eNB, RNs connected to the eNB, but this is not limitative.For example, the neighbor RN may include RNs connected to a differenteNB. In this case, by exchanging position information on the MBSFNsubframe used as the backhaul of RN connected to each eNB between eNBs,the same operation as in the present embodiment may be performed.

While description is given of an antenna in the above respectiveembodiments, the present invention is similarly applicable in the caseof an antenna port. The antenna port refers to a logical antennaincluding one or a plurality of physical antennas. That is, the antennaport does not always refer to one physical antenna, but may refer to anarray antenna or the like including a plurality of antennas. Forexample, in LTE, how many physical antennas an antenna port includes isnot defined, and reference signals of different base stations aredefined as minimum units that can be transmitted. Further, the antennaport is sometimes defined as a minimum unit that is multiplied by theweighting of a precoding vector.

Further, the functional blocks used for the description of theembodiment are typically implemented as an LSI which is an integratedcircuit. These may be individually formed as one chip or may be formedas one chip so as to include some or all. While an LSI is cited in thisdescription, it is sometimes called an IC, a system LSI, a super LSI oran ultra LSI according to the difference in integration degree.

Further, the method of circuit integration is not limited to an LSI, andthe functional blocks may be implemented as a dedicated circuit or ageneral purpose processor. After the manufacture of an LSI, aprogrammable FPGA (Field Programmable Gate Array) or a reconfigurableprocessor where the connection and setting of the circuit cells in theLSI are reconfigurable may be used.

Further, it is to be noted that when a circuit integration technologythat replaces the LSI appears by the progress of the semiconductortechnology or a derivative other technology, the functional blocks maybe integrated by using the technology. Biotechnology adaptation or thelike can be a possible example.

While the present invention has been described in detail with referenceto a specific embodiment, it is obvious to one of ordinary skill in theart that various changes and modifications may be added withoutdeparting from the spirit and scope of the present invention.

The present application is based on Japanese Patent Application(Japanese Patent Application No. 2009-139294) filed on Jun. 10, 2009,the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The radio communication terminal and radio communication methodaccording to the present invention have the following effects: thequality in communication with the handover destination can be measuredwith high accuracy, and the radio communication terminal is useful as aradio communication terminal.

REFERENCE SIGNS LIST

-   -   100, 500, 900 Radio communication terminal    -   101, 212 Antenna    -   103, 211 Reception RF section    -   107, 215 Reception processor    -   109 Neighbor cell signal reception processor    -   111 Measurement controller    -   113 Measurement subframe extractor    -   115 Measurement section    -   117 Measurement result memory section    -   119 Measurement report information generator    -   121, 207 Transmission processor    -   123, 209 Transmission RF section    -   200, 400 Base station (base station apparatus)    -   201 Measurement instruction section    -   203 Measurement information generator    -   205 Signal multiplexer    -   217 Measurement report information extractor    -   219 Handover controller    -   512 Measurement subframe detector    -   710 Measurement controller    -   711 Measurement candidate subframe extractor    -   712 RN group detector

The invention claimed is:
 1. A system comprising: a base stationcomprising a transmitter, which, in operation, transmits, to a terminal,control information, which, out of subframes including a first subframewith no transmission of data by another cell and a second subframe withtransmission of data by the another cell, indicates the second subframewith transmission of data by the another cell; and the terminalcomprising: a receiver, which, in operation, receives the controlinformation; and circuitry, which, in operation, measures a channelquality for the second subframe that said control information indicates.2. The system according to claim 1, wherein the another cell is neighborcell.
 3. The system according to claim 1, wherein the another cellcauses interference.
 4. The system according to claim 1, wherein saidcontrol information indicates a subframe other than a MBSFN(Multicast/Broadcast over Single Frequency Network) subframe.
 5. Thesystem according to claim 1, wherein said control information indicatesthe second subframe, out of subframes including the first subframe withno transmission of data by the another cell and the second subframe withtransmission of data by the another cell, as being bit mapped.
 6. Thesystem according to claim 1, wherein said control information indicatesthe second subframe, out of subframes including the first subframe withno transmission of data by the another cell and the second subframe withtransmission of data by the another cell, as being patterned.
 7. Thesystem according to claim 1, wherein the subframes that said controlinformation indicates are different depending on a cell.
 8. The systemaccording to claim 1, wherein the channel quality is measured for asubframe, in which the another cell causes an interference, based onsaid control information.
 9. The system according to claim 1, whereinthe channel quality is a reception power that is measured.
 10. Thesystem according to claim 1, wherein the base station comprises areceiver, which, in operation, receives, from the terminal, the channelquality measured for the second subframe that said control informationindicates.
 11. The system according to claim 1, wherein the terminalcomprises a transmitter, which, in operation, transmits, to the basestation, the channel quality measured for the second subframe that saidcontrol information indicates.
 12. A communication method comprising:transmitting, from a base station to a terminal, control information,which, out of subframes including a first subframe with no transmissionof data by another cell and a second subframe with transmission of databy the another cell, indicates the second subframe with transmission ofdata by the another cell; measuring, at the terminal, a channel qualityfor the second subframe that said control information indicates; andtransmitting, from the terminal to the base station, the channel qualityfor the second subframe that said control information indicates.